1. Field of the Invention
The invention relates to compositions and methods of use for soil amendments and bioremediation. More particularly, the invention relates to compositions and methods of use of hydratable keratin and keratin hydrogels as soil amendments and nutrient sources for bioremediation.
2. Description of Related Art
Keratin is a protein characterized by the prevalence of cysteine which, when crosslinked, render most keratins insoluble and environmentally robust in that they are resistant to hydrolysis and dissolution. Nitrogen release from unmodified poultry feathers has been reported as being too slow for use as a greenhouse fertilizer (Williams and Nelson, 1992). But, production of a feather meal by pressurized steam treatment, which breaks disulfide bonds, results in an increased rate of nitrogen mineralization (Hadas and Kautsky, 1994; Choi and Nelson, 1996). Feather meal also releases organic sulfur as plant available SO42xe2x88x92(Wainwright et al., 1985). The availability of nitrogen may also be enhanced by microbial action by composting keratin material. Fertilizers have also utilized keratin materials after complete hydrolysis to component amino acids. Chelates of such amino acids have been used as trace element fertilizers (Baolin et al., 1995). Mineral-organic fertilizers have also been prepared by mixing minerals with keratin hydrolyzates.
A possible limitation on crude keratin fertilizer preparations is that it may enrich the soil with keratolytic fungi which may be pathogenic to man and animals (Wainwright et al., 1985). Leather meal as a keratin source is also problematic because of the possibility of incorporating tanning agents such as chromium. Feather meal is malodorous, but can be made odor-free and more easily composted by autoclave treatment (Choi and Nelson, 1996).
An adequate supply of water is essential for plant survival and control of soil hydration is required for optimal plant growth. A number of soil moisture systems require a monitoring system that regulates an external water supply. Examples of such systems are disclosed in U.S. Pat. Nos. 4,796,654 and 4,182,357. These systems require a considerable amount of equipment, which will in turn require maintenance. U.S. Pat. No. 5,814,123 discloses the addition of humectants to enhance soil water retention. A humectant is a compound or material that has an avidity for water and will promote the retention of water in the soil. However, under some circumstances such a compound may compete with plants for the moisture retained in the soil. There is a continuing need for materials that can both enhance water holding capability and promote the retention of the moisture content of soil.
Bioremediation of soil utilizes microorganisms to degrade environmental contaminants such as hydrocarbons and halogenated chemicals. The rate and extent of microbial degradation is limited by the availability of nutrients in the contaminated soil. Without added nutrients, the microbial degradation of environmental contaminants can take an undesirably long time. Even with a nutrient supply, in situ bioremediation can be a prolonged process and preferred characteristics of microbial nutrient sources are that they are long acting, resistant to leaching, and biodegradable such that undesirable residues from the nutrient source are not left in the remediated soil. Groundwater is also amenable to bioremediation and permeable bio-active barriers are used to act as in situ bioremediation filters (Sutherson, 1997). Desirable characteristics for such barrier constituents are water permeability and a non-leachable nutrient source for support of a microbial population.
Physical barriers are also used in containment of environmental contaminants. Hair has been proposed as a physical adsorbent for the remediation of oil spills. Keratin preparations have also been disclosed as adsorbents for heavy metals (Japanese Patent Abstracts JP53042281, JP4281856). Natural sorbents, including keratin, have been used as physical sorbents for heavy oil in bioremediation studies (Setti et al., 1999). The use of sorbents increased the rate of n-alkane degradation, possibly due to the formation of a water/cell/oil/sorbent interphase. Natural sorbents are preferred because of their biodegradability.
The present invention provides a soil amendment comprising a chemically modified oxidized keratin that upon hydration forms a hydroge. The keratin hydrogel can increase the water retention properties of soil and provide a source of organic and inorganic nutrients. The hydrogel can also support the remediation of contaminated soil and groundwater by adsorbing environmental toxins and/or providing a nutrient source for microorganisms capable of degrading the environmental toxins.
In the context of the present invention, the term xe2x80x9chydratable keratinxe2x80x9d and xe2x80x9chydratable keratin materialxe2x80x9d is a keratin or keratin material that when hydrated forms a hydrogel.
One aspect of the present invention is a soil amendment composition comprising an oxidized keratin hydrogel. The oxidized keratin includes sulfonate groups and is associated with one or more metal ion species. xe2x80x9cAssociationxe2x80x9d and xe2x80x9cassociatedxe2x80x9d are defined in regard to the interaction between oxidized keratin and metal ion species as including both ionic bonds, that is heteropolar bonds between a negative anion and a positive cation, and chelates, wherein a metal is bonded to another molecule by a covalent bonding process or a coordination based on the donation of a free electron pair of one atom. It is believed that the predominant bonding is ionic and involves the sulfonic acid residues of the oxidized keratin. In the practice of preferred embodiments of the invention, one may select any suitable metal ion depending on the particular application, or the particular needs of the soil to be treated. For example, soils that are depleted in potassium or other plant nutrients, or that may be depleted in a cation or metal such as iron or zinc, for example, useful for microbial growth would be treated with a soil amendment that contained one or more of those metals or cations. In preferred embodiments, the one or more metal ions or cations associated with the oxidized keratin may include, but are not limited to potassium, sodium, copper, zinc, manganese, magnesium, iron, calcium and combinations of these.
The keratin source for the soil amendment composition may be any suitable source of keratin, either a soft keratin or a hard keratin, and would include keratin derived from animal or human hair, feathers, leather, skin, fur, animal hooves, animal or human nails, beaks, claws, scales, feet and horns, and is preferably a keratin that includes oxidizable amino acids such as cystines. In certain embodiments, the soil amendment may also further comprise a preservative such as an antifungal agent. Preservatives for use in the practice of the invention would include, but are not limited to tetraalkylammonium hydroxide, glutaraldehyde or formalin, and in certain preferred embodiments tetraalkylammonium hydroxide is used.
The soil amendment keratin hydrogel composition may be made by the process comprising oxidizing disulfide bonds in a keratin material with an oxidizing agent to obtain a keratin solid having sulfonic acid residues. Any suitable oxidizing agent may be used in the practice of the invention, including, but not limited to hydrogen peroxide, alkali peroxides, peracids, perborates, percarbonates, persulfates, hypochlorite or chlorine dioxide, with hydrogen peroxide or peracetic acid being the most preferred for certain embodiments. The oxidized keratin solid is separated and mixed with a water-miscible solvent containing one or more metal ion or cationic species such that the one or more metal ions or cationic species become associated with the oxidized keratin solid. The water-miscible solvent may contain up to about 20 volume percent of water. The water-miscible solvent is substantially removed and the oxidized keratin is hydrated to form a hydrogel. Any suitable water miscible solvent known in the art may be used in the practice of the invention. Exemplary solvents include lower alkyl alcohols such as methanol, ethanol, isopropanol, t-butanol or n-propanol, for example. Other solvents that may be used include, but are not limited to tetrahydrofuran, acetone, or acetonitrile, and combinations. The foregoing solvents may be used with up to 20 volume percent of water.
Another aspect of the present invention is a process for making a hydratable keratinderived soil amendment material. The keratin material may be any suitable source of keratin, either a soft keratin or a hard keratin, and would include keratin derived from animal or human hair, feathers, leather, skin, fur, animal hooves, animal or human nails, beaks, claws, scales, feet and horns, and is preferably a keratin that includes ionizable amino acids. The process comprises the steps of oxidizing a keratin material in a first solution with an oxidizing agent such that a portion of the disulfide bonds of said keratin material are oxidized to form sulfonic acid residues and forms an oxidized keratin solid fraction. The oxidizing agent may be any suitable agent, including, but not limited to hydrogen peroxide, alkali peroxides, peracids, perborates, percarbonates, and persulfates. The oxidized keratin is separated as a solid fraction from the first solution and added to a second solution comprising one or more metal ions dissolved in an neutral or slightly alkaline water-miscible solvent. The water miscible solvent may be any suitable solvent and in certain embodiments is a lower alkyl alcohol selected from the group comprising methanol, ethanol, isopropanol, t-butanol or n-propanol, and combinations of these. Other solvents that may be used include, but are not limited to tetrahydrofuran, acetone, or acetonitrile, and combinations of these. The solvents may be used with up to 20 volume percent of water. The second solution containing the oxidized keratin is maintained for a time and temperature effective to cause an association between the oxidized keratin and said one or more metal ions. It is understood, of course, that the metal ion or other cation in the second solution will associate with the oxidized keratin material, and that one controls the types and amounts of ions so associated by adjusting the concentration of such ions in the second solution. The one or more metal ion or cationic species associated with the oxidized keratin may be any suitable ions and would include potassium, sodium, copper, zinc, manganese, magnesium and calcium. The second solution is subsequently substantially removed so as to obtain a hydratable keratin material. The process may further comprise hydrating the keratin material to form a hydrogel. It is also understood that hydration of the hydrogel may include water soluble materials that are taken up in the hydrogel with the water, and that such materials, including plant or microbial nutrients, for example, would leach out of the hydrogel over time.
One aspect of the invention is compositions and methods for increasing the water retention properties of soil. One such method comprises the addition of a hydratable keratin material as described herein to soil. The keratin material may contain sulfonate groups as described above, and may be associated with one or more metal ion or cationic species. In the practice of this method, one would normally mix the solid obtained after treatment with water-miscible organic solvent solution described above in a dried state with an appropriate amount of soil. The keratin material may also be at least partially hydrated prior to addition to the soil such that it is in a hydrogel state. The hydrogel may be added to soil in any appropriate amount. For certain embodiments, the hydrogel may contribute from 5% to about 95% of the total weight of the mixture. It is also understood that the keratin hydrogel material may serve as the total plant growth support for certain plants, particularly for use in potted plants and seedlings, or for the growth of epiphytes, for example. In certain embodiments, the keratin material may contribute from about 1% to about 25%, or from about 1% to about 10% or from about 1% to about 5% of the total weight of the hydrogel/soil mixture. The hydratable keratin material may also provide nitrogen to the soil upon microbial degradation of the keratin material.
Another aspect of the present invention is a method for providing trace metal nutrients to soil comprising addition to soil of a hydratable keratin material. The hydratable keratin material may contain sulfonate groups and be associated with a plurality of metal ions species, and may be provided to the soil in either a dried or hydrated (hydrogel) state. The plurality of metal ion species may include, but is not limited to potassium, sodium, copper, zinc, manganese, magnesium or calcium. Any metal or other ion that associates with the hydrogel material may also be added to the soil by this method. The hydratable keratin material may also provide nitrogen or other nutrients to the soil upon degradation of the keratin material.
An aspect of the present invention is also a method for supporting the bioremediation of soil comprising addition of a hydratable keratin material to soil, such that the keratin material provides a nutrient source for microorganisms capable of remediating soil contaminated with environmental toxins. The hydratable keratin materials may comprise sulfonate groups and be associated with one or more metal ion species, and may be added in a dried state, or the hydratable keratin material may be hydrated to form a hydrogel. In the practice of this embodiment, the contaminated soil may be left in place, and the keratin material added to it and mixed, or alternatively, the soil may be removed from the site of contamination and treated at a remote location. A bacterial culture capable of removing, digesting, or concentrating a toxin or contaminate may be added directly to the soil, it may pre-exist in the soil, or it may be added to the keratin material prior to application to a material in need of remediation. All such uses known to those of skill in the art would be encompassed by the spirit and scope of the appended claims.
Another aspect of the present invention is a method for the bioremediation of groundwater contaminated with environmental toxins by providing a microorganism nutrient source comprising a hydratable keratin material. The hydratable keratin material may comprise sulfonate groups and may be associated with one or more metal ion species. In the practice of the invention, contaminated water may be mixed with a dried hydratable keratin material or a hydrogel, or it may be contacted with a hydrated keratin hydrogel material as in an in-line filter, or in a vessel.
Other aspects of the invention include methods for reducing the migration of environmental toxins in soil and water by providing a barrier against movement of contaminated or contaminating materials. In the practice of the method, hydratable keratin materials that may contain sulfonate groups and be associated with one or more metal ion species, may be used as a barrier. In certain embodiments, to reduce or control migration of a soil contaminant, a ditch may be placed around a contaminated area and filled with keratin hydrogel material. This practice offers the advantage that as the keratin material may become contaminated, it can be easily removed and replaced with fresh keratin hydrogel material. In an alternative embodiment, reduction of the migration of environmental toxins in groundwater may utilize a permeable barrier which intersects the flow of a plume of toxins. The hydratable keratin material may also provide a nutrient source for microorganisms capable of remediating soil contaminated with environmental toxins.